The disclosure generally relates to an apparatus for processing fuel vapor that may be generated in a fuel tank.
In a practically used fuel processing apparatus, a canister may be connected to a fuel tank via a vapor path and may adsorb fuel vapor generated in the fuel tank. The canister may be further connected to an engine, such as an internal combustion engine of an automobile, via a purge path, so that an intake negative pressure generated by the operation of the engine may desorb the fuel vapor from the canister. Due to a demand for an improvement in terms of a processing ability of the fuel vapor processing apparatus, various studies have been made for an increase in the adsorption capacity of the canister and for an increase in the purge flow rate. However, the increase in the adsorption capacity of the canister and the increase in the purge flow rate may lead to an increase in the pressure loss of the canister at the time of purging. Therefore, the negative pressure applied to the fuel tank via the vapor path at the time of purging may increase to cause unfavorable deformation of the fuel tank. Further, if the fuel vapor generated in the fuel tank is directly drawn into the engine, the air fuel ratio of the engine may be disturbed. In view of this, it has been proposed to provide a cutoff valve in the vapor path. The cutoff valve may be closed at the time of purging so that no negative pressure equivalent to the purge negative pressure may be applied to the fuel tank. Japanese Laid-Open Patent Publication No. 8-100711 discloses an apparatus equipped with a valve serving as the cutoff valve.
However, the cutoff valve disclosed in Japanese Laid-Open Patent Application No. 8-100711 is a diaphragm valve having a diaphragm. The atmospheric pressure is necessary to be applied to a backpressure chamber partitioned by the diaphragm for the operation of the valve. For this purpose, a structure is employed to open the backpressure chamber to the atmosphere. As is well known, the fuel vapor processing apparatus is necessary to be designed so as not to cause leakage of fuel vapor into the atmosphere. In a structure of the cutoff valve of Japanese Laid-Open Patent Application No. 8-100711, a space into which the fuel vapor flows and a space opened to the atmosphere are positioned adjacent with each other with an intervention of the diaphragm. Therefore, there is a possibility that fuel vapor leaks into the atmosphere when the diaphragm has been accidentally damaged.
In view of the challenges discussed above, there is a need in the art for a technique of preventing potential leakage of fuel vapor into the atmosphere from a diaphragm valve.